The present invention pertains to power and free conveyor systems, and more particularly pertains to improved apparatus for transferring the conveying of a train of free trolleys from one powered conveying chain to another.
Power and free conveyor systems typically utilize a train of free trolleys that are interconnected with load bars and which are propelled along a track by means of one ore more powered conveying chains. The trolleys support carriers on which parts are conveyed from one location to another, and the trolley train is propelled by engagement of a power dog on a conveying chain with a driving dog on the leading trolley. To provide a change in conveying speed and/or job spacing, the trolley-carrier assembly is often transferred from one conveying chain to another while remaining on the same load supporting track. This requires that the drive dog on the leading trolley become disengaged from a power dog on the first chain, and that the trolley train be provided with sufficient momentum to propel it along the track to a location where it is adjacent a second conveying chain for engagement of a power dog thereon with the driving dog of the leading trolley.
Prior methods for effecting the transfer of a trolley-carrier assembly from one conveyor chain to another include use of an air cylinder which is actuated at an appropriate time for pushing the assembly toward the other chain, a drop section in a power track, and a transfer dog that is located on one of the trolleys and actuated for engagement with a power dog of the conveyor chain prior to disengagement of the driving dog of the leading trolley from another power dog on the chain. The use of air cylinders is unduly complicated and expensive, whereas use of drop sections in the power track is costly and is accompanied by problems with engineering. Prior actuatable transfer dogs have included components which project beyond the profile of the track and thus cause mounting or interference problems. For one reason or another, therefore, such prior transfer methods and apparatus have not proven altogether satisfactory.